The FBI warns that ranking cities based on crime data can be misleading because each city reports crimes differently and some crimes go unreported.

However, an increase in crime can have a significant negative impact on a population, according to a 2009 study by the Furman Center for Real Estate & Urban Policy at New York University. And Detroit's unsafe streets are aggravating the city's struggle to maintain its already-dwindling population, which has shrunk by 25% since 2000.

Source: CQ Presscompiled this index using data reported by the Federal Bureau of Investigation's"Crime in the United States 2011." *The crime index is a weighted average of six crime categories murder, rape, robbery, aggravated assault, burglary, and motor vehicle theft. The national rate is 1 and any number higher than that indicates a higher than average incidence of crime. **List includes cities with populations of 250,000 or more.